Power brake for hoisting drums



March 13, 19 51 v R. R. CROOKSTON 6 POWER BRAKE FOR HOISTING DRUMS} Filed May 13, 1948 3 Sheets- Sheet l 52 SI 65 l ATTORNEY.

March 1951 R. R. CROOKSTON- POWER BRAKE FOR uox swmc DRUMS s Sheets- Sheet 2 Filed May 13, 1948 24 FIG.

l l l ATTORNEY.

March 13, 1951 R. R. CROOKSTON 2,545,136

POWER BRAKE FOR HOISTING DRUMS Filed May 13, 1948 s Sheets-Sheet 3 AIR SUPPLY AIR SUPPLY 6 0-5017 510075: lonflNVENTOR.

ATTORNEY.

Patented Mar. 13, 1951 POWER BRAKE FOR HOISTING DRUMS Robert R. Crookston, Houston, Tex., assignor, by

mesne assignments, to Standard Oil Development Company, Elizabeth, N. J., a corporation of Delaware Application May 13, 1948, Serial No. 26,843

Claims. (0!. 188-82) The present application is a continuation-inpart of my application Serial No. 691,486, entitled "Brake Assembly, filed August 19, 1946, now Patent Number 2,489,449.

The present invention is directed to a braking device adapted to control the rotation of a hoisting drum while lowering a load supported by a wire line. More particularly, the present invention is directed to a brake assembly adapted to be operated either by power means or manually for controlling the rotation of a drum.

For example, in the drilling of a borehole by the rotary drilling method, the drill stem employed when drilling deep holes is so long that the total weight of thedrill stem is not allowed to rest on the drill bit and in such operations a part of the weight of the drill stem 'is taken by the travelling block which is suspended from the crown block of the derrick by the hoisting line which in turn has an end attached to the hoisting drum or draw works. For emcient operation, it is desirable that the load carried by the drill bit be relatively uniform. If insuflicient weight is carried on the bit, it does not penetrate as rapidly as is desirable while if the weight carried by the bit is excessive the hole produced may be crooked or the drill stem may be twisted off.

It is an object of the present invention to produce an arrangement which allows the speed of rotation of a hoisting drum to be accurately controlled while producing a minimum amount of shock and irregularity of movement of the hoisting drum.

It is a further object of the present invention to produce a device which is capable of closely controlling the speed of rotation of a hoisting drum carrying a heavy load supported by a line and which is capable of terminating the rotating movement substantially instantaneously whenever desired by the operator.

Another object of the present invention is to provide a brake assembly which may be activated at any time by power means or manually at the option of the operator.

Other objects and advantages of the present invention may be seen from the following description taken in conjunction With the drawing in which Fig. 1 is a front elevation showing the embodiment of the present invention;

Fig. 2 is a side elevation partly in section taken along line IL- II of Fig. 1.

Fig. 3 is a fragmentary view taken along line III-III of Fig. 2.

- the valve in the conduit. The device is further Fig. 4 is a fragmentary view taken along line IVIV of Fig. 3.-

Fig. 5 is a view showing in detail the construction of a valve of the assembly of Fig. 1.

Fig. 6 is a view showing in detail the movable element of the valve shown in Fig. 5; and

Fig. '7 is a view showing in detail the construction of a valve of the assembly of Fig. 1.

Fig. 8 is an elevation of a portion of the device shown in Fig. 1.

Fig. 9 is a sectional view showing construction of a bearing assembly of Fig. 1.

Fig. 10 is a flow diagram showing the conduits fluidly connecting the various parts of the apparatus illustrated in Fig. 1.

The device of the preesnt invention may be described briefly as involving two brake bands mounted on a frame supporting a hoisting drum with the brake bands mounted for limited arcuate movement and mechanically linked together so that they are in fixed relationship with each other at all times. Line may be paid out from the hoisting drum at a controlled rate under normal operations with one brake band loose and the other tight on the drum andcontrol means arranged to be activated by power and control means adapted to be activated manually are provided, said control means'each being capable of tightening both of the bands simultaneously to stop completely the rotation of the hoisting drum.

In its more specific aspects, the device of the present invention involves two brake bands mounted on a frame supporting a hoisting drum.

The brake bands are arranged for limited arcuate movement with the axis of the movement of the bands coinciding with the axis of rotation of the hoisting drum and the brake bands are mechanically connected so that they are in fixed relationship with each other at all times. Two cylinders with a piston arranged in each cylinder are mounted on the frame with one of the cylinders connected to one of the brake bands and the other cylinder connected to the other brake band. Conduits fluidly connect like ends of the cylinders and valve means is arranged in at least one of the conduits whereby movement of a piston in one of the cylinders forces the piston in the other cylinder to move in the other direction in response to hydraulic pressure and the speed of the movement is controllable by provided with a mechanical linkage connecting the two brake bands and maintaining the brake bands in fixed positionwith respect to each other.

As long as the hydraulic means is in working order the mechanical linkage is unnecessary but if the hydraulic system loses fluid, for example, the mechanical linkage connecting the two brake bands insures that the tightening simultaneously of both brake bands either through the power means or the manual means instantly stops the rotation of the hoisting drum.

Means are provided for contracting the brake bands in turn whereby a first brake band is lockedto the hoisting drum and moves through its predetermined arc while the second brake band is loose and moves in the opposite direction; when the first brake band has moved through its predetermined arc, the second brake band is contracted to lock it to the hoisting drum and substantially simultaneously the first brake band is released, the second brake band then moves with the hoisting drum while the first brake band is returned to its original position. When the second brakeband has moved throughits predetermined arc, the first brake band is locked to the hoisting drum and the second brake band released and the cycle repeated.

The device or the present invention is arranged so that oth. brake bands may be contracted simultan;o..sly to stop completely the rotation of the hoisting drum. This may be done either by power means or manually. The operation of wholly stopping the rotation of the hoisting drum either by power means or manually is separate from the hydraulic control means which regulates the speedat which the drum rotates in the normal operation of paying out drilling line so that after the drum has been completely stopped it may subsequently be returned to normal operation at the same speed of rotation.

The present application is an improvement over the device described and claimed in my copending application Ser. No. 691,486, filed August 19, 1946, now Patent Number 2,489,449, issued May 12, 1949, in that it incorporates the additional feature of a positive mechanical linkage between the two brake bands which maintains these bands in fixed relationship with each other at all times and supplements the hydraulic system so that even though a mishap occurs with respect to the hydraulic system the brakes may be set to stop instantly the rotation of the hoisting drum. It may be noted that for purposes of simplifying the description of the present drawing, parts of the control means are shown in a more simplified form than shown in Ser. No. 691,486. Certain parts of the valve mechanism are also described and claimed in my copending application Ser. No. 693,992, entitled Valve Assembly, filed August 30, 1946, now Patent Number 2,489,450, issued November 29, 1949.

Turning now specifically to the drawing, the apparatus will first be described generally. A frame A has a drum assembly B mounted thereon for rotation about a fixed axis. The frame and drum assembly may be a conventional hoisting apparatus or draw works. Mounted on drum assembly B are brake band assemblies C and C. Portions of brake band assemblies C and. C are connected to form a complete hydraulic system. Brake band assemblies C and C are mechanicallyconnected to assembly D which is mounted on the frame and serves to keep the assemblies C and C in fixed relationship at all times. Corresponding portions of brake band assemblies C and C are connected with system E; system E including parts shown within the dashed rec- ,rtangle Figs. 1 and 6. The system E may be .de-,

scribed as a power means for operating assemblies C and C" and is adapted to operate through the medium of a compressible fluid maintained at superatmospheric pressure. This compressible fluid may be such a material as air, nitrogen or flue gas but for convenience hereinafter in this specification it will be referred to as compressed air.

A hand brake assembly F is mounted on frame A and is arranged for applying a braking force to the brake drum assembly for emergency operation. It will be noted that in Fig. 2 a rope or line ll is .carmed. by drum assembly B; this illustrates the normal operation of the device which isadapted to pay out the line. However, in order to bring out the construction of the device more satisfactorily in Fig. 1 a showing of line H has been omitted therefrom.

Drum assembly B is mounted on frame A for rotation about a fixed axis indicated by numeral t2 in Fig. Drumzrassembly B defines cylindrical surfaces l3' and i3 adaptedto cooperate with brake band assemblies. C' and C, respectively. Drum assembly B vcomprise's'a cylindrical surface I'll between the brake band assemblies arranged for: receiving the line H in the usual manner.

By reference to Fig. 2,.brake band assembly C will beseen tou'i-nclude arcuate band 15 and arcuate band Hi with ends of the band held together with adjustable clamp H. A power unit comprising cylinder [8, piston i9 arranged to reciprocate therein, and piston rod 20 with one end attached to piston 19 and projecting through the piston rod end of cylinder 18', is mounted by trunnions 2 I' toplates 22 carried by arcuate member 15. A spring I9 is located in the head end of cylinder l8- andtends :to bias piston [9 toward the piston rod endof cylinder 18. The end of piston rod 29 is fastened through pin 23 to link 24 which has its other end secured to arcuate member 15 by pin 25; Lever 24 is pierced to receive a pin 26 which serves to attach an end of link 21 to link 24. Link 21 is also attached through pin 28 to clevis 29 which,'inturn, is secured to the end of arcuate member it through pin 39. Pin 28 also serves .to attach clevis 29 and link 21-to lin-k 3| which, in turn, is secured to arcuate member l5 through pin- 32.

A cylinder 33,.with its lower end secured to trame A, has a piston slidably mounted therein. Pistonrod35 isattached tothe piston 34 and projects through the piston rod end of the cylinder. Piston rod 35 is secured to a projection 36 of arcuate member I5 by pin 31!. It may be noted that the arrangement of cylinder 33 withpiston 34 mechanically connected to arcuate member l5 serves as a hold-down for the brake band when force is applied by means of piston 1'9 and cylinder l8.

Brake band assemblies C and C are exactly alike with the parts ofassembly C identified by numerals, and corresponding parts of assembly C identified with corresponding primed numerals. Accordingly, the individual parts of assembly C will not be separately listed.

Aslong as the hydraulic system is in good working order the hold-down provided by pistons 34- and34 are in good working condition, but in order to make the mechanical braking assembly independent of the hydraulic system, brake band C is mechanically connected to equalizer assembly D by means of bolt 38 passing through an opening defined in projection and the brake .band'C" is similarly connected to equalizer assembly D by means of bolt 38.;

spherical bearing links 43' and as. v cal bearing links are used to connect the connect- Assembly D consists of a single tree 40 pivoted by bearing 4| to frame A. One end of the single tree is connected to brake band C by connecting rod 42 with the end of the rod connected to an end of the single tree by a suitable spherical bearing link 43 while the upper end of the rod is connected to projection 36 of band assembly C by spherical bearing link 44. Similarly, brake band assembly C is connected to the other end of the single tree by connecting rod 42' through The spheriing rod with the single tree in order to provide the necessary two plane oscillation for the connecting rods 42 and 42. The single tree 46 defines slots 45 and 45' arranged adjacent corresponding projections 46 and 46 of frame A so that when it is desirable to maintain thesingle tree stationary, as when replacing hydraulic fluid in the system, a single tree may be locked to theframe by inserting pins, not shown, through slots 45 and 45' for engagement with projections 46 and 46 respectively. When single tree 46 is locked against oscillatory movement brake band C and C cannot move arcuately in opposite directions.

The parts making up auxiliary hand brake assembly F are shown in Figs. 1, 2, and 3. This assembly includes parallel shafts i and 52; shaft 5! is journaled to frame A through journals 53 and 54 and shaft 52 is journaled to the frame by journals 55 and 56. The hand lever 51 is mounted on the outboard end of shaft 5|. A pair of crank arms 58 is mounted on shaft 5i for rotation therewith and a pair of crank arms 49 is mounted on shaft 52 for rotation therewith; the ends of these pairs of crank arms are connected together through link 66. A second pair of crank arms 6| is also mounted on shaft 52 for rotation therewith, said crank arms being linked through members 62 and 63 and bolt 64 to equalizer 65. The lower surface of equalizer 65 is in slidable contact with frame A.

One end of equalizer 65 is connected through chain 65 to arcuate member 16 of brake band assembly C while the other end of equalizer mem ber is connected through chains 66' to arcuate member iii of brake band assembly C". It will be seen that When the lever arm is in the position shown in the drawings, the chains 66 and 66 are slack thereby allowing the brake assemblies C and C" to be operated by compressed air without bringing the hand operated brake into play. Movement of hand lever 51 to rotate shaft 5| in a clockwise direction as viewed in Fig. 2 will first take up the slack in chains 66 and 66' and then tighten the brake assemblies 0 and C against surfaces I3 and I3, respectively, of the hoisting drum.

The piston rod ends of cylinders 33 and 33 of assemblies C and C are fluidly connected by conduit 6'! having an orifice therein shown as an adjustable needle valve 68. The conduit 61 is also connected fluidly to an accumulator 69. accumulator is provided in the hydraulic system to make allowance for the lack of perfect phase relationship between the mechanical linkage including assembly D and the hydraulic system. This slight discrepancy is caused by the necessary movement of the connecting rods 42 and 42 in two planes while link 43 is oscillated in one plane and the link 34 is moved arcuately.

In the hydraulic system under normal operating conditions the piston rod connected to the band which is tight on the brake forces its piston The 6' upwardly in the cylinder and this forces fluid through conduit 61 into the other cylinder. For example, if the brake band of assembly C is tight on the hoisting drum piston 34 is moved upwardly and forces hydraulic fluid through conduit 61 into the head end of cylinder 33 where the fluid pressure forces the assembly C' to move downwardly. The speed of this movement is controlled by the setting of needle valve 68.

It is not necessary for the head ends of cylinders 33 and 33 to contain a liquid but in order to provide for smoothness of operation it is desirable to connect these parts fluidly as by conduit 16 and provides liquid in this part of the system. If the head ends of the cylinder contain liquid and if it be assumed that piston 34 is being forced upwardly, liquid from the piston rod end of cylinder 33 is displaced through conduit 10 to the.

head end of cylinder 33. During the other phase of the operation of the device when assembly C is tight on the drum and assembly C is'loose,

fluid is forced from the piston rod end of cylinder 33 through conduit 67 into the piston rod end of cylinder 33 and in turn forces the assembly C" to move downwardly while at the same time fluid is displaced from the head end of cylinder 33 through conduit in to the head end of cylinder 33. In assembly C a valve member H is mounted on the piston rod end of cylinder 33 and a means 12 for operating the valve member is mounted on piston rod 35. ll is mounted on the piston rod end of cylinder 33 and a means 12 for operating the valve member is mounted on piston rod 35. Valves H and H are a portion of the control assembly E which will now be described.

The assembly E for supplying and controlling the flow of compressed air into cylinders 18 and I8 of brake band assembly C and C includes a valve assembly consisting of valve a, valve b and a diaphragm c arranged to connect mechanically the movable valve elements of valves 0. and 1). Valve a is arranged to control the operation of brake band assembly 0 while valve bis arranged to control the operation of brake band assembly 0. When the device of the present invention is paying out line in its normal operations, the operation of the assembly consisting of valves 41. and b and diaphragm c is controlled by valves H and H but when the power means is employed to cause both brake band assemblies 0 and C to grip the drum B simultaneously, the valve assemblies a and b are activated by diaphragm c.

Valve :1 consists of a valve housing 8| with a slidable valve element 82 mounted thereon. Slidable valve element 82 defines a passage 83 and a passage 84. Housing 8| defines an inlet port 85 and outlet ports 86 and 87 while the head end of the housing defines a port 88. When valve element 82 is in the position with respect'to housing 8! shown in Fig. 5 and hereinafter referred to as its first position, the base of fluid passage 83 is in fluid communication with inlet 85 of the housing and the upper portion of the passage is fluidly connected to outlet 86; however, in this position passage 84, hereinafter referred to as an exhaust passage, does not have fluid communication with any ports of the housing. When the valve element 82 is at the other end of the valve housing, a position hereinafter referred to as its second position, fluidpassage 83 has no communication with the ports of the Similarly, in assembly C valve 7" able. valvelmember laz is connected to red 89 passing through a suitable fiuid-tight gland, not shovvnin detail,.ot the housing v8 Valve '1) corresponds :to valve a except that the positions of the various parts: are reversed, that is .to say, the two valves a and b are related in the same way asnthe right and left hands of. a person. In: valve b'housingS i has slidable member 82 arranged therein. Member 82 defines passages 83' and "84, the. housing .8!" defines inlet passage 8.5, outlet passages 85. and 8?." and the head of the housing defines a port 88.

Iislidable. member 82: is in the position shown in Fig; 7,. hereinafter referred to as its second position, exhaust passage 84' is in communication with .ports 86. and 81' so :that air can exhaust throughthe valve- If the sliclablev member 82" is atthe. other end of housing 8 l, a position. hereinafter referred to as its first position, passage. :83 is. in communication with ports .85 and 86 so that air can pass through the valve. Slidable valve element 32: is connected to rod 89. which passes through a suitable fluid-tight gland, not shown in detail, of housing 3|".

The. valve members 82 and 82 are mechanically connected through diaphragm whereby the two slidable members are retained in .a fixed relative position during what is hereinafter referred to as normal operation while the spacing betweenthe two members 82 and 82' is altered in what is hereinafter referred to as an emergency operation.

Rod '89 is attached to one side of diaphragm .c and rod 89 is attached to the opposite side of diaphragm c. Aninlet air line 9!! controlled by valve in is fluidly connected to diaphragm member 0. Air line 90 is provided with a bleeder valve 94 to release the pressure from diaphragmc.

A conduit 92 fluid-1y connects valve H with port 88 of valve 2) While conduit 92 connects port 88 of. valve (1 with valve H. An inlet line 93 is adapted to connect an inlet port of valve H with a suitable source of compressed air, not shown on the drawing, and similarly an inlet line 93 is adapted to connect valve H to a suitable source of compressed air, not shown on the drawing.

When the drum B is paying out line at rate which is controlled by the hydraulic system, the position of the movable valve elements in valves a and c are controlled by the operationoi valves H and- I l which in turn are activated by contact with members 12 and 1'2 carried by brake band assemblie C and C. However, when the operation departs from normal, as when it is desired to stop the rotation of the hoisting drum entirely, the movable elements in valves a and a are con-trolled by air pressure applied to diaphragm 0 through conduit 9! controlled by valve 9|.

The operation of the device shown in the drawing will now be described in greater detail. It will first be assumed that the device is operating to pay out drilling line with the operation to be controlled by the hydraulic system. In starting the discussion it will be assumed that the parts of'the apparatus are in the position shown in Fig. 1 with valve 9! closed. It will also be assumed that in'valve a the valvemember 82 is in its first position and in valve member 22 valve member 82' is in its second position. With this valve setting compressed air is applied to the piston rod end of cylinder l8 and brake band assembly C is tight on the drum and the rotation 8 of therirum is moving operating means 12 away from valve 11, while air is exhausted vfrom the piston rod end of cylinder 18 and brake band assembly C is loose on the drum and activatin member .12 is. being moved toward valve H As the drum continues to rotate, activating member 1-2 is brought into contact with valve H and opens it to allow compressed air to flow through conduit 2 to the head end of valve a where the air pressure imposed on. valve element 82 moves it from its first to its second position and the thrust transmitted through rod 89', diaphragm c and rod 89 moves the valve element 82' in valve b from its second position to its first position. Upon the movement of elements in valves a, b, and diaphragm c, compressed air is applied to the piston rod end of cylinder l8 and is exhausted from the piston rod end of cylinder l8. That is to say, before the elements in valves a and b are moved, assembly C is tight and assembly C is loose on the hoisting drum B but after the. movement of the valve elements brake band assembly C is tight and brake band assembly C is loose on brake drum B. The drum B continues to rotate under the tension exerted by the drilling line and with this rotation the activating member #2 of brake band assembly C moves towardvalve I! while the activating member 12' carried by brake band assembly C is moved out of contact with the valve H. This operation insures that the valves H and TI. will be activated only a short time and after the compressed air has accomplished its purpose of changing the setting of the assembly consisting of valves a, b and diaphragm c either by passing through valve .ll or valve H, the valve will be shut off. When the. hoisting drum B brings contacting member 12 into contact with valve "H air pressure is admitted through this valve and passes through conduit. 92 to the head end of valve 1). The admission of air pressure to the end of valve 22 forces valve element 82' to move from its first position to its second position and the thrust is exerted from the element through rod 83, diaphragm c androd 89 to valve element 82 of valve on and moves. element 8.2 from its second position toi'ts first. position. This movement of the valve allows air to be exhausted from the piston rod end of cylinder 1'8" and allows compressed air to be admitted to the piston rod end of cylinder is; this action of the valves releases brake band assembly 0 and contracts brake assembly C. The device is now in the position described at the beginning of the cycle which will be continually repeated under normal operations.

When rotation of the drum isv to be stopped by the use of compressed air, it is merely neces- .d-rives member 82' from its second to its first position while valve member 82 is retained in its first posit-ion. Similarly, as the assembly has been in normal position with valve member 82 in its first position and valve 82 in its second position, the "expansion of diaphragm 0 drives valve member -82 to its first position while valve member 82 is retained in its first position. The

efiect of theexpansion of diaphragm c is to allow compressed air to pass simultaneously through valves a and b to the piston rod ends of cylinders l8 and I8 causing both brake band assemblies C and C to engage hoisting drum B.

The device may be returned from emergency operations to normal operations by closing valve 9| and bleeding air from the conduit 90 through bleeder valve 94.

The assembly of the present invention is adapted to employ air pressure in the normal operations of the brakes. However, means are provided so that the brakes may be applied manually at any time. When the brakes are to be operated manually, the operator or driller applies force by means of a hand lever 51. In the views shown in Fig. 2, rotation of the shaft in a clockwise direction transmits energy through the linkages to shaft 52 causing it to rotate in a counterclockwise direction and in turn transmittingthe force through members 62, 63, 64, and 65 through chain 66 and 66'. This rotation of the shaft by the hand lever will first take up the slack in chains 66 and 6S and will then tighten brake band assemblies C and C' against the surfaces [3 and I3 of the hoisting drum.

As long as the hydraulic system remains intact, the arrangement of the cylinders 33 and 33' with their pistons 34 and 34' provides a holddown means for the assemblies C and C whereby the tightening of the brakes either by the use of air pressure operating pistons l9 and I9 sembly F be redesigned to compensate for such additional movement or else possibly be inoperative should a mishap occur. The possibility of such an occurrence is eliminated by the arrangement of the assembly D which mechanically connects the brake assemblies C and C through the single tree 40. The assembly D provides a mechanical linkage between the brake band assemblies C and C at all times so that even though fluid would be lost from the hydraulic system the brakes may be set instantly by the use of hand lever 51. The reason for this is that the mechanical connection betwen brake band assemblies C and C through assembly D positively limits the movements of the two assemblies and even though fluid be lost from the hydraulic system the brake band assemblies C and C are fixed in relationship to each other so that the slack which must be taken up in chains 66 and 66' is always a constant value.

While I have described a specific embodiment of the present invention, it will be obvious to a workman skilled in the art that various changes in the sizes and proportions of the several parts may be made as desired.

Having fully described and illustrated a prefaces of brake band comprising, in combination, a first brake band mounted on the frame for restricted arcuate movement about an axis coinciding with the axis of the hoisting drum, a second brake band mounted on the frame for restricted arcuate movement about an axis coinciding with the axis of the hoisting drum, first power activated means adapted for engaging said first brake band with the drum, second power activated means for engaging said second brake band with the drum, switching means for activating said first and second brake bands either simultaneously or alternatively, a lever, means pivoting the center of the lever to said frame, a first linkage oscillatable in two planes connecting an end of said lever to said first brake band and a second linkage oscillatable in two planes mechanically connecting the other end of said lever to said second brake band.

2. A brake band assembly comprising, in combination, a hoisting drum mounted on a frame for rotation about a fixed axis and defining at least a first and second symmetrical surface adapted for engagement with friction brake members, a first brake member mounted on the frame for restricted arcuate movement about an axis coinciding with the axis of the hoisting drum, power activated means arranged for engaging said brake member with and disengaging it from a cylindrical surface of said hoisting drum, a second brake member mounted on the frame for restricted arcuate movement about second brake member with and disengaging it from the second surface defined by the Hoisting drum, a hand operated brake lever, a mechanical linkage arranged to engage simultaneously said first and'second brake members with said first and second friction surfaces of the hoisting drum upon operation of said hand lever, a lever, means pivoting the lever at its center portion with said frame, a first linkage oscillatable in two planes mechanically connecting one end of said lever with the first brake member and a linkage oscillatable in two planes mechanically connecting the other end of said lever with said second brake member.

3. A device in accordance with claim 2 in which'the symmetrical surfaces defined by the hoisting drum are cylindrical in shape and in which the first and second brake members are brake bands. 7

4. A brake assembly adapted to be applied to a hoisting drum mounted on a frame for rotation about a fixed axis and defining cylindrical surfaces adapted to be engaged with friction surfaces of brake bands comprising, in combination, a first brake band mounted on the frame for. restricted arcuate movement about an axis coinciding with the axis of the hoisting drum, a second brake band mounted on the frame for restricted arcuate movement about an axis of the hoisting drum, first power activated means adapted for selectively engaging said first brake band with the drum, second power activated means adapted for selectively engaging said second brake band with the drum, switching means for activating said first and second brake bands either simultaneously or alternatively, a lever, means pivoting the center of the lever to said frame, a first linkage connecting an end of said lever to said first brake band and a second linkage mechanically connecting the other end of said lever to said second brake band.

151 r 5-; Abrake bandzassembly comprising, in com-:- binatiom aal hoistingdrum; mounted" on; a; frame for rotation about a; fixed:- axis; and; defining; at least. afirst? and: second; symmetricalsurface adapted. for engagement with friction, brake members, a first brakemember; mounted-:on the framerfor restrictedtarcuate=movement about an axis: coinciding with the axis. of. the hoisting dr.um,- power: activated means arranged" for engaging said brakee-memberiwith and disengaging it from; a cylindrical: surface of said hoisting drum, a second bral ze member mounted on; the frame ion-restrictediarcuate imovement: aboutian axiscoinciding. with. the axis of: the; hoisting drum, at-power means arrangedforengaging said second brake member with. and." disengaging; it from; the. second: surfacedefined; by; the; hoisting drum, a handoperatedbrake lever, a mechanical and'second frictionsurfaces of the hoistin :drum

'12 upomoperation ofisaid hand1ever,- a-r lever rmeans pivotingthe; lever ate itsicentert portion: with said frame; a: first linkage; mechanically connecting oneend of 'saidzlever'withthe first brake memher and a linkage" mechanically connecting the otheraend' of said lever-with said'secondbrake member.

ROBERT R. CROOKSTON.

REFEBENGE S. CITED The following references are of record in the file of this patent:

UNITEDvv STATES PATIENTS 15 N m am ate--v 1,910,805 MacClatOhiQ May-v23: 1933 1;932,-685; Blach- Get; 31; 1933 956,433 Young et-al. Ap1. 24, 1934 2,195,200 Bloss t Mar. 26-, 1940 20 2,371,851 Stevenson Mar; 20, 1945 

